[Talk-us] Special issues in LA remap
Alan_Mintz+OSM at Earthlink.Net
Wed Jun 13 16:31:06 BST 2012
At 2012-06-07 16:39, Mike N wrote:
> Using way id 13292685 : http://www.openstreetmap.org/browse/way/13292685
> , I looked at the edits. In this case, some nodes were moved, presumably
> to align with the aerial imagery. I couldn't find any GPS tracks in the
> immediate area to confirm the aerial alignment. The node I looked at
> was moved at least 10 meters.
> A fast preemptive remap for nodes set for redaction-move would be to
> just move the node to align with current Bing aerial. Note that the
> Bing aerial alignment might not be perfect - try to find some GPS tracks
> in the area to see how close it is. There should be some tracks on the
> nearest interstate.
This is a non-issue in southern CA. I've done enough calibration against
high-accuracy benchmarks in the area to believe that Bing imagery is
uniformly within 2m of true. OTOH, GPS tracks, especially from an antenna
inside a moving vehicle, are much less accurate than that.
> So, the redaction bot will not completely destroy those areas. If no
> one has touched the road alignment since his work, it will just revert
> back to the original TIGER upload coordinates. All that is required
> after the redaction bot will be to nudge the nodes to the location where
> they belong.
10m is a big shift. If the errors were that big in this area, I would bet
that if you looked at the original TIGER05 import, it would look like a
toddlers scrawl compared to the look of the map now. I've seen untouched
areas before that were that bad, so I know what it looks like. "All that is
required" will be a huge amount of work to re-align thousands of ways. It
seems far easier to look at them, compare against the imagery, and
pronounce them accurate, and I'd like to get a real legal opinion from
someone involved with the licensing on whether the latter approach would be
sufficient. Can we do that?
Alan Mintz <Alan_Mintz+OSM at Earthlink.net>
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